I'm an experienced artist, i grew up with drawing so I know what I'm talking about
anyway, I know for a fact that it takes really good practice and skill to draw the way these following titles:

Air Gear :: The artist seems to exel at drawing in different perspectives that most artists cant do at all
D. Gray-Man :: Nicely detailed, not overdone
Kateikyoushi Hitman Reborn :: A favorite for the most epic detailed fighting scenes Evar.
Saiyuki :: Obviously its difficult enough to reproduce the style of this manga
07 Ghost :: Detailed, Clean,drawn in a very cool style